Load Balancer unhealthy and CDK deploy stuck

I have a loadbalancer and a fargate service, which I deploy after another from CDK.

First problem is that the cdk deployment is not going through (see images below).

Second problem which could be the reason for the former is that the health check is failing, although the container health check works and when I set the loadbalancer to be accessible from the internet I could perform my health check and got "OK" with code 200 back.. target health check fails

container is healthy

My steps: 1: loadbalancer

    const relayerLoadBalancer = new elbv2.ApplicationLoadBalancer(
      this,
      "RelayerLoadBalancer",
      {
        vpc: vpc,
        internetFacing: false,
      }
    );

    this.relayerLoadBalancer = relayerLoadBalancer;

2: Taskdefinition and Container from Ecr (see gist)

3: relayer Service with Fargate (also in gist):

    const listener = props.relayerLoadBalancer.addListener("RelayerListener", {
        port: 80,
        protocol: elbv2.ApplicationProtocol.HTTP,
        open: true,
      });
  
      listener.connections.allowFromAnyIpv4(ec2.Port.allTraffic());
  
    const sg_service = new ec2.SecurityGroup(this, "RelayerSG", {
      vpc: vpc,
      allowAllOutbound: true,
      description: "Security group for Relayer tasks",
    });
    sg_service.addIngressRule(
      ec2.Peer.ipv4("0.0.0.0/0"),
      ec2.Port.allTraffic()
    );

    // Create a Fargate service
    const relayerService = new ecs.FargateService(this, "RelayerServiceM", {
      cluster: cluster,
      taskDefinition: props.taskDefinition,
      enableExecuteCommand: true,
      securityGroups: [sg_service],
      assignPublicIp: false,
      healthCheckGracePeriod: Duration.seconds(3600),
    });

    listener.addTargets("RelayerTarget", {
      port: 80,
      targets: [relayerService],
      healthCheck: {
        path: "/health",
        healthyHttpCodes: "200-499",
      },
    });

Ive tried to split the load balancer and fargate service but the cdk deployment is always stuck (for example: step 4/6) in the step where the service is created:

stuck cdk deployment image

Therefore the deployment in the console is also in progress: aws console image

I think maybe the cdk deploy fails because the health check fails but maybe also the health check fail because the deployment doesnt go through. Sounds confusing and I definitely am.

I've set the healthCheckGracePeriod to 5h, which should be more than enough time for the health checks to come through...

I've read something about that the health check must not be performed on the port 80 but since Ive opened up all traffic this shouldn't be a problem right?